~ 

GENERAL TECHNICAL REPORT PNW-159 

1983 

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BIGHORN SHEEP 

. WALTER A. VAN DYKE 

ALAN SANDS 

JIM YOAKUM 

ALLAN POLENZ 

JAMES BLAISDELL 

PACIFIC NORTHWEST FOREST AND RANGE EXPERIMENT STATION 

FOREST SERVICE U.S. DEPARTMENT OF AGRICULTURE 
Abstract 

Habitat in southeastern Oregon that was 

used by California bighorn sheep until about 

1916 can be managed to maintain herds t hat 

have been reintroduced into the area and to 

accommodate additional herds. Survival and 

productivity are enhanced by management 

based on an understanding of the animal's 

needs. These include appropriate interspersion 

of adequate water, forage, and escape terrain, 

lack of competition with other grazing ungulates for food and water, and absence of 

disturbance. 

The Authors 

WALTER A. VAN DYKE is Wildlife 

Biologist, Oregon Department of Fish and 

Wildlife, Enterprise, Oregon. ALAN SANDS is 

Wildlife Biologist, U.S. Department of the Interior, Bureau of Land Management, Boise, 

Idaho. JIM YOAKUM is Wildlife Biologist, U.S. 

Department of the Interior, Bureau of Land 

Management, Reno, Nevada. ALLAN POLENZ 

is Wildlife Biologist, Oregon Department. of 

Fish and Wildlife, Hines, Oregon. JAMES 

BLAISDELL is Wildlife Biologist (Retired), 

U.S. Department of the Interior, National Park 

service, Friday Harbor, Washington. 
This publication is part of the series Wildlife 

Habitats in Managed Rangelands-The Great 

Basin of Southeastern Oregon. The purpose of 

the series is to provide a range manager with 

the necessary information on wildlife and its relationship to habitat conditions in managed 

rangelands in order that the manager may 

make fully informed decisions. 

The information in this series is specific to 

the Great Basin of southeastern Oregon and is 

generally applicable to the shrub-steppe areas 

of the Western United States. The principles 

and processes described, however, are generally 

applicable to all managed rangelands. The purpose of the series is to provide specific information for a particular area but in doing so to 

develop a process for considering the welfare of 

wildlife when range management decisions are 

made. 

The series is composed of 14 separate publications designed to form a comprehensive 

whole. Although each part will be an independent treatment of a specific subject, when combined in sequence, the individual parts will be 

as chapters in a book. 

Individual parts will be printed as they become available. In this way the information will 

be more quickly available to potential users. 

This means, however, that the sequence of 

printing will not be in the same order as the 

final organization of the separates into a comprehensive whole. 

A list of the publications in the series, their 

current availability, and their final organization is shown on the inside back cover of this 

publication. 

Wildlife Habitats in Managed RangelandsThe Great Basin of Southeastern Oregon is a 

cooperative effort of the USDA Forest Service, 

Pacific Northwest Forest and Range Experiment Station, and United States Department of 

the Interior, Bureau of Land Management. 
Introduction 

Bighorn sheep1 were once abundant 

throughout Western North America. Since 

1900, however, they have declined in most areas 

(fig. 1) and many populations have been eliminated (Buechner 1960, Wagner 1978). Population declines have been attributed to hunting, 

to parasites and disease, and to competition 

with domestic livestock for forage, and with humans for space (Buechner 1960, Davis and 

Taylor 1939, Honess 1942, Honess and Frost 

1942, Packard 1946). Wildlife agencies in the 

western regions of Canada, the United States, 

and Mexico have initiated programs to maintain or enhance existing populations of bighorn 

sheep and to reintroduce them into historic 

ranges (Spalding and Mitchell1970, Trefethan 

1975). But, unless there is better land management, a decline of 8 percent can be expected in 

the next 25 years on land managed by the 

Bureau of Land Management (BLM), U.S. Department of the Interior (Jahn and Trefethen 

1978). 

1 Scientific and common names and their sources 

are listed in the appendix. 

In the Great Basin the situation is somewhat 

different. Although some transplant attempts 

have failed (Trefethan 1975), the States have 

been successful in reintroducing bighorn sheep 

into some historic ranges (Trefethan 1975, 

Yoakum 1973). 

Three subspecies of bighorn sheep were endemic to the Great Basin in the past: Rocky 

Mountain, California, and desert bighorns 

(Bailey 1936, Buechner 1960, Cowen 1940, Hall 

and Kelson 1959, Seton 1929). The California 

bighorn sheep, indigenous to the southeastern 

Oregon portion of the Great Basin, disappeared 

around 1916 (Bailey 1936). As a result of transplants, the area again has several populations 

of California bighorn sheep (Trefethan 1975). If 

these once-native sheep are to remain, it is essential to maintain or enhance habitats that 

meet their biological requirements. 

Bighorn sheep have evolved unique social 

and behavioral traits. They occupy traditional 

ranges and are slow to pioneer new habitats 

(Geist 1971). This means that careful manageIOD I _________________________ ___, 

· •• · • · ·· ·.. Dor.u;o~op c, 

·· .... ···· ... ~~-~""1' 

· .. ··. 

-------------·------. __ VIi-lOR... 

1.,00 1.,10 I~'ZD 1,~ l~o l'!lo 1'}1>0 f'JO l'&o 

Figure I.-Grazing of wild ungulates has declined in 

the western United States since 1850 while grazing 

of domestic ungulates has increased (redrawn from 

Wagner 1978:137). 

1 
ment of the habitat of existing herds is critical. 

Much habitat used by herds in the past is publicly administered and is suitable for additional 

transplant attempts (Yoakum 1971, 1973). 

Some publicly administered habitat, however, 

is now unsuitable because of past abuse 

(McCutchen 1981). Management techniques 

are available to make these areas again suitable for bighorn sheep, and interim management 

should not preclude opportunities to reestablish 

herds in the future. 

Our purpose is to help land and wildlife managers evaluate, maintain, and enhance habitat 

for bighorn sheep by providing information that 

will enable them to: (1) recognize potential 

habitat on the basis of geomorphic features and 

plant communities; (2) predict the consequences 

of management actions; and (3) select appropriate management alternatives. 

Information in this chapter was developed 

specifically for California bighorn sheep habitat 

in the Great Basin of southeastern Oregon. Few 

scientific studies of bighorn sheep habitat and 

management have been made in that part of the 

Great Basin. Consequently, we have used some 

information from other areas of the Great Basin 

or from other regions. Because such studies 

have frequently dealt with the desert or Rocky 

Mountain subspecies, the information presented here should have application to all 

bighorn sheep, with appropriate local 

adjustments. 

We have made the following assumptions: 

1. Extensive areas of historic habitat, presently unoccupied by bighorn sheep, can support herds or can be made capable of supporting 

herds. 

2. Land uses can be tailored to provide areas 

of sufficient size to maintain viable populations. 

3. Where there are conflicts between 

bighorn sheep and other ungulates for forage, 

water, or cover on public land, it may be necessary to give priority to bighorn sheep. 

4. The information presented here is concerned with maintaining natural populations of 

free-ranging wild sheep; we are not addressing 

situations where populations can be maintained only by artificial means. 

2 

Characteristics of Habitat 

Bighorn sheep generally inhabit remote 

steep, rugged terrain, such as mountains, can~ yons, and escarpments where precipitation is 

low and evaporation is high (fig. 2). Plant communities are usually low and open in structure 

and stable, at or near climax. Sagebrush/grassland steppes and cold desert shrublands are the 

dominant types. 

Bighorn sheep ranges in southeastern Oregon include several plant communities (Dealy 

et al. 1981) that reflect variations in elevation ' slope, aspect, soil type, and precipitation (fig. 3). 

Summer ranges vary from subalpine meadows 

or grasslands at elevations above 2 287 meters 

(7 ,500 ft), to sagebrush/ grasslands or shrublands that are dominant at elevations above 

1 220 meters (4,000 ft). Winter ranges are usually, below 1 830 meters (6,000 ft) and are 

characterized by shrub/ grasslands or shrublands. Communities dominated by trees or tall 

shrubs such as aspen, cottonwood, fir, pine, 

juniper, mountainmahogany, squaw apple, and 

cherry, may occur throughout both summer and 

winter ranges, but there are no large densely 

forested areas. 

Some bighorn sheep herds are year-long residents on a given area, with little or no spatial 

separation of summer and winter ranges (Blood 

1963a, Drewek 1970, Demarchi and Mitchell 

1973, Haas 1979, Kornet 1978, Van Dyke 1978). 

Oth~r herds migrate several miles between 

summer and winter ranges and occupy areas 

that include a variety of elevations and environmental conditions (Blood 1963a, Geist 1971, 

Shannon et al. 1975). Both summer and winter 

ranges must provide freedom from disturbance 

and a proper juxtaposition of forage, escape terrain, and water if viable populations are to be 

maintained. 

The major needs ofbighorn sheep are: forage, 

water, thermal protection, and areas for escape, 

rutting, and lambing. If forage, water, andescape terrain are available, varying amounts of 

thermal protection will also be provided and 

rutting and lambing will normally occur. There 

are, however, cases where bighorn sheep move 

to particular areas to rut or lamb (Geist 1971, 

Kornet 1978). Management should not interfere with this movement. 
Figure 2.-Mountains, canyons, and escarpments 

provide bighorn sheep habitat. 

Figure 3.- An example of bighorn sheep habitat in 

southeastern Oregon (photo by Walt Van Dyke). 

3 
ESCAPE AREAS 

Cliffs, rock rims, rock outcroppings, and 

bluffs typify escape habitat, which is primarily 

used for bedding (Davis and Taylor 1939, Hailey 

1971, Hansen 1980, Kornet 1978, Van Dyke 

1978) and for escape from perceived danger 

(Frisina 1974, Geist 1971, Hansen 1980, Leslie 

and Douglas 1979, Woolf 1968). Steep broken 

cliffs with traversable terraces are desirable; 

sheer, vertical cliffs are not (fig. 4). Where cliffs 

are lacking, steep slopes are used for escape 

\ 

1 

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(Demarchi and Mitchell 1973). Unstable 

geomorphic features such as talus are also used 

for escape and bedding. 

We have no specific data on sizes of cliffs suitable for bedding and·escape areas. We have estimated minimum size requirements on the basis 

of criteria provided by Maser et al. (1979). The 

importance of cliffs varies with size (fig. 5). For 

example, cliffs that provide thermal cover, bedsites, and escape terrain may not be large 

enough for lambing. 

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Figure 4.-Comparison of vertical and terraced cliffs 

as escape terrain for bighorn sheep. 

4 
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Figure 5.--Size determines the importance of cliffs 

as habitat for bedding, escape, and lambing. 

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5 
Cliffs less than 8 meters (26 ft) high by 200 

meters (656 ft) long can provide both bedding 

and thermal areas because they offer some 

shade in summer and reflect the sun or dissipate 

absorbed heat in winter. To provide escape terrain cliffs must be at least 8 meters (26 ft) high 

by 200 meters (656 ft) long or larger (Bailey 

1980, McCollough et al. 1980). A series of 

smaller cliffs with less than 10 meters (33ft) between them effectively equals a larger cliff. 

Another way to evaluate cliffs is on the basis of 

area. Cliffs 0.16 hectare (0.4 acre) and larger 

can serve as escape terrain as well as bedding 

and thermal areas, whereas smaller cliffs provide only thermal and bedding areas. To suffice 

as a lambing area, a cliff or series of cliffs must 

be at least 2 hectares (5 acres). 

Cliffs provide sparse forage and are used for 

foraging, particularly during lambing season 

(Van Dyke 1978) and in winter, when forage in 

adjacent cliffless habitat is unavailable because 

of crusted snow and ice (Baumann and Stevens 

1978, Geist 1971, Geist and Petocz 1977, Shannon et al. 1975). Cliffs do not accumulate as 

much snow as flatter areas; they reradiate sunrays that melt snow and keep it soft, making it 

easier for bighorn sheep to paw away snow to 

obtain forage. 

Ewe-lamb groups prefer more rugged topography than ram groups (Blood 1963a, Drewek 

1970, Leslie and Douglas 1979) and are more restricted in use of their range (Geist 1971, Leslie 

and Douglas 1979, Van Dyke 1978). Ram 

groups will range farther from escape terrain 

than ewe-lamb groups (Leslie and Douglas 

1979). This behavior may be related to their reproductive roles (Geist 1971). Escape terrain 

may be located above, below, or beside forage 

and water areas because bighorns can move up 

or down easily from bedsites to such areas. 

The distribution of escape terrain regulates 

the extent to which other habitat components 

are used. Most bighorn sheep use forage areas 

within 0.8 kilometers (0.5 mi) of escape terrain 

and generally are not seen farther than 1.6 

kilometers (1 mi) from escape terrain (Bailey 

1980, Denniston 1965, Drewek 1970, Kornet 

1978, Leslie and Douglas 1979, McQuivey 1978, 

Oldemeyereta1.1971, VanDyke 1978). Sources 

6 

of water more than 0.5 kilometer (0.3 mi) from 

escape terrain receive limited use (Leslie and 

Douglas 1979). Distances may increase or 

decrease, depending on the magnitude and 

frequency of disturbance sheep receive from 

humans or predators. In general, use decreases 

as the distance from escape terrain increases. 

(fig. 6). 

LAMBING AREAS 

Terrain commonly used for lambing is rugged, precipitous and remote (Drewek 1970, 

Geist 1971, Irvine 1969, Van Dyke 1978) (fig. 

7). Such terrain provides pregnant ewes security and isolation for the lambing period, which 

includes the time lambs need to become strong 

enough to follow the ewes. Large cliffs and rock 

outcroppings with sparse cover of trees or 

shrubs, such as mountainmahogany, afford 

both thermal and hiding cover to ewes and 

lambs (Van Dyke 1978). Ideally, adequate forage and water are found within or near lambing 

areas so ewes with young lambs do not have to 

venture far to water or forage (Light et al. 1966, 

1967). Ewe-lamb groups stay in lambing areas 

for about a month after lambing before venturing into adjoining, less rugged habitats (Geist 

1971, Van Dyke 1978). 

Use of lambing areas is frequently traditional but may be altered by lingering deep 

snow or insufficient forage or water. Lambing 

occurs on winter, summer, or spring-fall ranges, 

depending on prevailing environmental conditions, the location of a pregnant ewe at the critical time, and the nature of the available terrain. 

The birthplace is usually secluded and in rugged terrain. A ewe may travel several kilometers 

to such an area to give birth (Geist 1971). 

Ruggedness and remoteness influence the 

size of areas required for lambing. If 

harassment is great, a larger area is more desirable. Ewes appear to select rugged cliffs of at 

least 2 hectares (5 acres) with dimensions of at 

least 80 meters (262ft) by 260 meters (853ft). 

Several ewes may lamb within one such area. 

Adequate size of an area for lambing depends 

on outside influences. For example, in remote, 

extremely rugged topography, where harassment is low, only 1 hectare (2.5 acres) may be 

sufficient. 
HIC:lH 

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Figure 6.-Distance from escape terrain determines 

the extent of use . 

..... ... .., .. -. .. ".J:">. 

Figure 7 .-Large areas of rugged terrain are preferred for lambing (photo by Walt Van Dyke, courtesy 

Oregon Cooperative Wildlife Research Unit). 

7 
Figure 8.-Plant.communities that provide open, low 

structure are sUitable forage areas (photo by Walt 

Van Dyke, courtesy Oregon Cooperative Wildlife Research Unit). 

FORAGE AREAS 

Bighorn sheep tend to forage in open areas 

with low vegetation, such as grasslands, shrublands, or mixes of these (Geist 1971, Hansen 

1980, Sugden 1961, Van Dyke 1978) (fig. 8). Perennial bunchgrasses, which make up a large 

part of bighorn diet (Barrett 1964, Blood 1967, 

Browning and Monson 1980, Constan 1972, Demarchi 1965, Geist 1971, McQuivey 1978, Pitt 

and Wikeem 1978, Sugden 1961, Todd 1972) are 

an important characteristic of these areas. 

The importance of grass in a bighorn sheep's 

diet was substantiated by a study that compared plant consumption in the Great Basin of 

Nevada to plant availability (Yoakum 1964). 

On a year-long basis, more grass was consumed 

(59 percent) than forbs (32 percent), and shrubs 

(9 percent) (fig. 9). These percentages are 

noteworthy because a diet primarily of grass 

was selected from a cold desert where shrubs 

predominated. Similar findings were reported 

by Barrett (1964) in Nevada. 

8 

A variety of plant species, common to southeastern Oregon, provide important forage for 

bighorn sheep (table 1). Lists of plant species 

can be used to predict the importance of areas 

for forage, but amounts consumed by bighorn 

sheep will vary with species composition, range 

condition, and plant productivity. 

Although grass is a staple of the bighorn 

sheep's diet, a variety of browse and forbs are 

also used seasonally in varying amounts 

(Johnson and Smith 1980, Todd 1972). On some 

ranges where grass or forbs are sparse, diets 

may consist primarily of browse (Howard and 

Lorenzo 1975). For the most part, bighorn sheep 

seem to be opportunistic foragers and, if the 

physical structure of the habitat is appropriate, 

can adapt their diet to available plant communities-whether they are dominated by 

grass, forbs, or shrubs (Browning and Monson 

1980, Robinson and Cronemiller 1954). 
YEtJE:TATIVE. 

C0Ml'061DON 

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Figure 9.-Comparison of vegetative composition 

and percent volume of forage classes represented in 

12 rumen samples from bighorn sheep on the Silver 

Peak range, Nevada. (Redrawn from Yoakum 1964) 

Table 1-Plants common to the Great Basin of southeastern Oreg·on and their seasonal occurrence 

in the diet of bighorn sheep1 

Plant species by Level ofuse2 

forage class Winter Spring Summer Fall 

Grasses: 

Bearded bluebunch wheatgrass H H M M 

Idaho fescue M M L M 

Bluegrass L H M M 

Bottlebrush squirrel tail L L L 

Prairie june grass L M L L 

Pine grass L L L M 

Indian rice grass M M M 

Giant wildrye M M M L 

Cheat grass L M 

Sedge L M M L 

Thurber's needlegrass M M L M 

Meadow barley M 

Forbs: 

Arrow leafbalsamroot L M L 

Phlox L L 

Mil kvetch L L L 

Lupine L L L L 

Cushion buckwheat M M 

Buckwheat L L L L 

Penstemon L L 

Lomatium M M 

Erigeron M M 

9 
Table !-Continued 

Plant species by 

forage class 

Cobre rock cress 

W est~rn tansymustard 

Daggerpod 

Yarrow 

Trees and shrubs: 

Big sagebrush 

Low sagebrush 

Bud sagebrush 

Winterfat 

Rabbitbrush 

Fourwing saltbush 

Bitter brush 

Mountainmahogany 

Service berry 

Elderberry 

Chokecherry 

Spiraea 

Wildrose 

Ninebark 

Currant 

Cinquefoil 

Willow 

Snow berry 

Oceanspray 

Spiny hopsage 

Winter 

L 

M 

M 

M 

M 

L 

M 

H 

H 

L 

L 

L 

L 

M 

L 

L 

L 

Level ofuse2 

Spring Summer 

M M 

L 

M 

L L 

L L 

M 

L 

M M 

L L 

L L 

H M 

M L 

L M 

L 

L L 

L M 

L M 

M M 

L M 

L M 

L L 

Fall 

L 

M 

H 

L 

M 

M 

L 

L 

L 

L 

L 

L 

L 

M 

M 

L 

L 

M 

1 Adapted from Blood (1967), Cooperrider et al. (1980), Drewek (1970), Dunaway (1972), Estes (1979), 

Fairaizl (1978), Hansen (1982), Kornet (1978), Lauer and Peek (1976), McCullough and Schneegas 

(1966), Pitt and Wikeem (1978), Sugden (1961), Todd (1972), Van Dyke (1978), Yoakum (1966). 

2 L = light, 1 to 5 percent; M = moderate, 6 to 20 percent; H = heavy, 21 to 50+ percent. 

10 
Production of forage depends on the amount 

and timing of precipitation. Managers can estimate the amount of forage available for bighorn 

sheep only after deducting for plant needs and 

the amount to be used by other grazing animals. 

Forage intake ofbighorn sheep is determined 

by their energy requirements and the availability and quality of forage (Hebert 1973). The 

amount needed varies with protein content, ambient air temperature, and the sex, age, and 

activity level of the animal. Apparently consumption does not vary markedly from year to 

year. Few studies have been conducted to determine the amount of forage required by bighorn 

sheep, but estimates have been made by Anderson and Denton (1978), Hansen (1980), and 

Hebert (1973). Such estimates should be used 

only as a guide in southeastern Oregon and 

should be updated as more data become 

available. 

Hansen (1980) found that desert bighorn 

sheep consumed from 1.5 to 1.8 kilograms (3 to 

4 lbs) of dry alfalfa per day. Anderson and Denton (1978) in Idaho, and Hebert (1973) in British 

Columbia, figured the year-round average intake for Rocky Mountain bighorn sheep was 

1.44 kilograms per 45.40 kilograms of body 

weight (3.17 lbs per 100 lbs). A bighorn sheep 

with an average weight of56.4 kilograms (124 

lbs) would consume 1. 77 kilograms (3.90 lbs) of 

dry matter each day. Once the percentages of 

grasses, forbs, and shrubs in the diet of sheep 

are known and the percentages of each that can 

be provided by the plant communities are 

known, a more accurate computation of forage 

available can be made. 

Because they depend largely on their acute 

vision to detect danger, bighorn sheep shun 

areas of dense, tall vegetation, such as riparian 

zones and forests (Geist 1971, Kornet 1978, 

McCann 1956, Oldemeyer et al. 1971, 

Risenhoover and Bailey 1980, Turner and 

Weaver 1980) (fig. 10). They avoid extensive 

forage areas with shrub or canopy cover in excess of25 percent and shrubs about 60 centimeters (2ft) high on mild slopes (Van Dyke 1978), 

whereas, on steep slopes they have been noted 

to travel through and bed in dense brush (Light 

et al. 1967). 

The availability of water and escape terrain 

also affects use of forage areas. The more abundant and evenly dispersed these components 

are, the more uniform use of a forage area will 

be. Forage areas located farther than 0.8 

kilometers (0.5 mi) from escape terrain and 

farther than 1.6 kilometers (1 mi) from water 

are little used (Bailey 1980, Blong and Pollard 

1968, Denniston 1965, Irvine 1969, Kornet 

1978, Leslie and Douglas 1979, McQuivey 1978, 

Oldemeyer et al. 1971, Van Dyke 1978). 

Snow accumulation seems to be the principal 

factor that triggers bighorn sheep to move from 

summer to winter ranges (Geist 1971, Geist and 

Petocz 1977). Where winter and year-long 

ranges accumulate snow, animals seek areas of 

least snow depth and paw away snow to uncover 

forage (Drewek 1970, Geist 1971, Geist and 

Petocz 1977, Shannon et al. 1975). In Idaho, 

Lauer and Peek (1976) found that from 

November through May, 87 percent of bighorn 

sheep sightings were in areas with less than 5 

centimeters (2 inches) of snow, and 97 percent 

were in areas with less than 16 centimeters (6 

inches). 

Bighorn sheep prefer green forage and will 

move up or down or to different aspects to acquire more palatable forage (Hebert 1973, 

Lauer and Peek 1976, McCann 1956, Shannon 

et al. 1975, Van Dyke 1978). 

Forage areas that present a variety of aspects 

are preferable because they provide green forage for longer periods. For example, south aspects are generally warmer and provide green 

forage earlier in spring, while north aspects are 

generally cooler and provide green forage later 

in summer. Because they are warmer, south 

aspects generally have less snow during winter 

and are selected by bighorn sheep (Bailey 1980, 

Drewek 1970, Lauer and Peek 1976, Light et al. 

1967, McCollough et al. 1980, Van Dyke 1978). 

Suitable versus Unsuitable Forage Areas 

It is difficult to classify forage areas as suitable or unsuitable solely on the basis of plant 

species composition. 'lbpography, substrate, 

vegetative structure, distance to escape terrain 

11 
r""' 

Figure 10.-Bighorn sheep prefer open areas and 

shun tall dense stands of trees or shrubs (photo by 

Walt Van Dyke, courtesy Oregon Cooperative 

Wildlife Research Unit). 

and water, snow depth, and season are also important. Forage areas suitable for bighorn 

sheep usually have tree or shrub canopy cover 

of less than 25 percent and shrub height less 

than 0.6 meters (2 ft). They are less than 1.6 

kilometers (1 mi) from water and less than 0.8 

kilometers (0.5 mi) from escape terrain. If the 

above criteria are met, any of the plant communities of southeastern Oregon can provide 

some forage. 

We have rated the major plant communities (in 

the order listed by Dealy et al. (1981)) according 

to their suitability as forage for bighorn sheep. 

On a scale of 1 (low) to 10 (high), ratings are: 

Plant Community 

Riparian 

Quaking aspen/grass 

Quaking aspen/mountain big sagebrush 

Curlleaf mountainmahogany /mountain big 

sagebrush/bunchgrass 

12 

Rating 

5 

2 

2 

5 

Curlleafmountainmahogany/mountain 

snow berry/grass 

Curlleaf mountainmahogany /Idaho fescue 

Curlleaf mountainmahogany /bearded 

blue bunch wheatgrass-Idaho fescue 

Curlleafmountainmahogany/pinegrass 

Western juniper /big sagebrush/bearded 

bluebunch wheatgrass 

Western juniper/big sagebrush/Idaho fescue 

Basin big sagebrush/bunchgrass 

Mountain big sagebrush/bunchgrass 

Subalpine big sagebrush/bunchgrass 

Wyoming big sagebrush/bunchgrass 

Three-tip sagebrush/bunchgrass 

Bolander silver sagebrush/bunchgrass 

Mountain silver sagebrush/bunchgrass 

Stiff sagebrush/bunchgrass 

Low sagebrush/bunchgrass 

Cleftleaf sagebrush/bunchgrass 

Black sagebrush/bunchgrass 

Early low sagebrush/bunchgrass 

Squaw apple/bunchgrass 

Black greasewood/bunchgrass 

Shadscale saltbush/bunchgrass 

Meadow, seasonally wet 

Meadow, permanently wet 

Subalpine bunchgrass 

4 

4 

4 

3 

6 

6 

7 

9 

9 

8 

1 

1 

1 

7 

7 

1 

7 

7 

2 

1 

3 

10 

8 

10 
Several plant communities in the Great 

Basin seldom provide forage because of their 

structure or distance from escape terrain. Communities unsuitable because of structure are: 

quaking aspen, mountainmahogany, western 

juniper, and riparian communities dominated 

by tall shrubs or trees. Communities usually located far from escape terrain and little used for 

foraging include: squaw apple/bunchgrass, 

black greasewood/grass, early low sagebrush/ 

bunchgrass, black sagebrush/bunchgrass, Bolander silver sagebrush/bunchgrass, mountain 

silver sagebrush/bunchgrass, threetip sagebrush/bunchgrass, shadscale saltbush/bunchgrass, and cleftleaf sagebrush/bunchgrass. 

These communities will get incidental use 

along migration routes or within established 

herd ranges. 

Successional communities that result from 

wildfire or seedings, such as crested wheatgrass, are also encountered in the Great Basin 

and may provide forage if the location and successional/sera! structure are appropriate. 

Summer versus Winter Range 

The variation in elevation and topography in 

the Great Basin creates microsites that differ in 

accumulations of snow. Some areas may be 

available for foraging only during a 3-month 

summer period before snow depth precludes 

use. In such cases, bighorn sheep may establish 

patterns of seasonal use of such areas. 

Other areas suitable for foraging may accumulate little or no snow and receive year-long 

use. Areas that provide suitable forage yearround are particularly vulnerable to overuse because of competition among a variety of wild or 

domestic herbivores. 

WATER 

Bighorn sheep use fresh water from many 

sources. These include dew, streams, lakes, 

springs, ponds, catchment tanks, troughs, 

guzzlers, and developed seeps or springs (Blong 

and Pollard 1968, Drewek 1970, Halloran and 

Deming 1958, Jones et al. 1957, Sugden 1961, 

Turner and Weaver 1980, Van Dyke 1978, Welles and Welles 1961, Yoakum et al. 1980). Alkaline waters, however, apparently are not 

suitable (Jones et al. 1957). Although the degree of alkalinity tolerated by bighorn sheep is 

unknown, the maximum dissolved solids suitable for ungulate wildlife has been described as 

4,500 p /m (McKee and Wolf 1963). We assume 

that this figure also applies to bighorn sheep. 

The amount of water needed by a bighorn 

sheep depends on several factors, including: size 

of the animal, activities, time between waterings, physiological adaptation, environmental 

stress (humidity and temperature), succulence 

of ingested forage, and reproductive status 

('furner and Weaver 1980). A bighorn sheep ingesting succulent forage on a cool day requires 

little or no free water, whereas one ingesting 

dry forage on a hot day needs more free water 

('furner and Weaver 1980). There is a greater 

need for water during periods of physiological 

stress, such as during rutting or lambing seasons (Wilson 1968). 

- Desert bighorn sheep have been known to go 

without water for more than 5 days during summer (Turner and Weaver 1980). They may drink 

as little water per day as 4 percent of their body 

weight and as much as 23 percent of their body 

weight at one time (Turner 1973, 'furner a nd 

Weaver 1980). Koplin (1960) found that a captive herd of desert bighorn sheep that were fed a 

dry ration and provided unlimited water drank 

an average of 4.91iters (1.3 gal) per day, while 

free-ranging bighorns were observed to drink as 

much as 9.5 liters (2.5 gal) per day during summer. Frequency of watering and succulence of 

vegetation both influence water consumption. 

A reasonable estimate of the minimum amount 

of water needed by free-ranging, adult California bighorn sheep of average size (56.4 kilograms, 124lbs), is 3.5liters (1.5 gal) per day. 

Bighorn sheep spend most of their time 

within 1.6 kilometers (1 mi) of free water but 

have been located as far as 3.2 kilometers (2 mi) 

from it (Blong and Pollard 1968, Irvine 1969, 

Leslie and Douglas 1979). Water sources more 

than 0.5 kilometer (0.3 mi) from escape terrain 

or surrounded by tall dense vegetation are 

shunned by bighorn sheep (Hansen 1980, Leslie 

and Douglas 1979, 'furner and Weaver 1980). 

13 
As the number of water sources declines, 

habitat use becomes more confined around remaining water sources (Jones et al. 1957, Leslie 

and Douglas 1979, Welles and Welles 1961). 

But as precipitation, new plant growth, and 

cooler temperatures reduce dependence on permanent water, the animals can temporarily extend their range (Leslie and Douglas 1979). 

THERMAL PROTECTION 

Elevation, thermal winds, cliffs and rock outcroppings, and trees and shrubs, provide animals the opportunity to minimize stress caused 

by temperature extremes (fig. 11). Some 

bighorn sheep herds move to higher elevations 

in summer because of available forage and a 

cooler environment (McCann 1956, Shannon et 

al. 1975). On subalpine summer ranges where 

winds were consistent bighorn sheep used little 

shade.2 Where summer ranges are below the 

subalpine zone, bighorn sheep seek shade from 

geomorphic features to moderate the effects of 

high temperatures (Leslie and Douglas 1979, 

Welles and Welles 1961). The amount of energy 

bighorn sheep expend in thermoregulation will 

be reduced if the geomorphic features offer a 

variety of aspects, thus increasing the amount 

of shade available at different times of day. 

2 Van Dyke, Walter A., wildlife biologist. 1978 

data on file at Oregon Department of Fish and 

Wildlife, Enterprise, Oregon 97828. 

Figure 11.-Cliffs, trees, and shrubs provide shade. 

14 
Shrubs and trees with dense canopies provide varying degrees of thermal cover for deer 

and elk (Thomas et al. 1976). Bighorn sheep 

normally occupy open areas and consequently 

do not benefit from the thermal protection offered by tall, dense-canopied vegetation, but 

they do use trees and shrubs to some extent for 

this purpose (Hansen 1980, Smith 1954). Mountainmahogany stands, with 25-percent canopy 

cover, located on cliffs or ground steeper than 

35 percent, are apparently used for protection 

from the sun, especially by ewes during lambing 

season (Van Dyke 1978). Habitats with dense 

canopy cover on gentle slopes (less than 35 percent) are used less or even avoided, probably because sheep have poor visibility from within 

such stands (Van Dyke 1978). In general, use of 

~ \\ ~ \ 

Figure 12.-Caves provide thermal cover and lambing sites. 

trees and shrubs for thermal cover is positively 

correlated with slope and roughness of terrain 

and negatively correlated with increasing 

canopy cover, density, and distance from escape 

terrain. 

Cliffs and rock outcroppings provide shade 

on hot days and reflect solar radiation during 

co~d periods. Bighorn sheep seek shade during 

m1dday and thus conserve body water (Leslie 

and Douglas 1979) and enhance metabolic efficiency (Moen 1973). Caves are sometimes used 

for this purpose (Hansen 1980, Leslie and Douglas 1979, Welles and Welles 1961) as well as 

for lambing (Fairaizl 1978, Hansen 1980) and 

for shelter during severe storms (Smith 1954) 

(fig. 12). 

15 
RUTTING AREAS 

A bighorn sheep herd usually has discrete 

areas within its range where breeding occurs. A 

herd may move to traditional rutting areas (Demarchi and Mitchell1973, Geist 1971) or rams 

may move to ewe-lamb ranges (Kornet 1978, 

Van Dyke 1978) for the rut. 

During the rut, which occurs from late October to mid-December, the need for forage and 

water changes. For example, bighorn sheep forage less when rutting (Geist and Petocz 1977) 

but require more water than usual (Wilson 

1968). 

ARRANGEMENT OF HABITAT COMPONENTS 

Forage, water, and escape terrain are the 

most important components of bighorn sheep 

habitat, but the size, quality, and distribution 

of these components are also important. In the 

best habitats, water sources and escape terrain 

are distributed throughout foraging areas and 

thus make more grazing available. This intermingling of habitat components reduces pressure on forage near water and escape routes 

and helps prevent degradation of plant 

communities. 

Forage areas within 0.8 kilometer (0.5 mi) of 

escape terrain on two or more sides receive more 

frequent and uniform use than forage areas 

with escape terrain on only one side (fig. 13). 

Figure 13.-Uniform distribution of sufficient escape 

terrain is important to bighorn sheep. In A three different escape routes are available; in B only one; consequently, sheep will forage closer to escape terrain 

in B than in A. 

16 
The location of water also influences use of 

forage areas. If water is distributed at intervals 

of 3.2 kilometers (2 mi) or less throughout a 

range and is not farther than 0.5 kilometer 

(0.3 mi) from escape terrain, optimum use of the 

habitat can be expected. Sheep will then forage 

in a circuit, covering more area and putting less 

grazing pressure on desirable portions of the 

area. 

SPACE REQUIREMENTS 

Bighorn sheep require more than the essential components of appropriately arranged 

habitat. They also need space. Hansen (1980:7 4) 

described space as" ... a lack of crowding." The 

amount of space needed depends on quality of 

habitat, the amount of negative impact from humans and other animals, and the size of the 

bighorn herd. Trefethan (1975) suggested that 

a minimum herd size of 125 animals is necessary for a long-term, viable population. The 

area required by such a herd depends on the 

quality of the habitat. Kornet (1978) and Van 

Dyke (1980) have calculated minimum densities of 13 bighorns per square kilometer (5/sq 

mi) for herds in the Great Basin of southeastern 

Oregon. These figures can be used as a guide for 

estimating the population potential of a given 

habitat but may exceed the capacity of poorer 

quality habitat. 

Individuals of every bighorn sheep population apparently vary in their tolerance of crowding. For example, individual Rocky Mountain 

bighorn sheep accustomed to people in a N ationa} Park can be photographed from a car window, but individuals unaccustomed to people 

may flee at the sight of a person or vehicle a mile 

or more away. Once the limit of tolerance is exceeded, even in otherwise optimum habitat, 

sheep may abandon an area temporarily or permanently (Light 1971, Spalding and Bone 1969, 

Wehausen 1980, Welles and Welles 1961). Although bighorn sheep are naturally gregarious, 

crowding can be detrimental. Crowding may 

result from a lack of suitable habitat, snow accumulation, structural condition of plant communities, presence of other ungulates, or 

harassment by humans or predators. The 

amount of space needed by bighorn sheep varies 

with habitat conditions and size of the population. Adverse effects on a sheeJP population are 

indicated by abandonment of an area, a drop in 

productivity, or excessive mortality. 

Productivity and survival are enhanced by 

appropriate interspersion of adequate water, 

forage areas, and escape terraiDl, as well as sufficient space, to allow bighorlfl sheep to use 

habitat efficiently and minimize energy expenditures and exposure to disturbance. 

Management 1rips 

The attributes of bighorn sheep habitat can 

be created, preserved, destroyE!d, or altered by 

management action. 

ESCAPE AREAS 

" Escape terrain is provided naturally by the 

environment. Without it bighorn sheep will not 

flourish (Hansen 1980). Rarely can it be enhanced, but it can be altered detrimentally by 

such activities as mining and constructing 

roads and reservoirs (fig. 14). In many cases, 

physical alterations are much less important 

than the disturbance these alterations introduce. For example, human use of a road along or 

through a lambing or bedding area eliminates 

the solitude needed by sheep1. Likewise, development of a large reservoir may allow 

human access by boat to areas formerly remote 

and inaccessible. 

LAMBING AREAS 

The relatively isolated and rugged cliffs cannot be created, but other attributes of prime 

lambing habitat can be enhanc1ed. Size oflambing areas can be increased by manipulation of 

adjacent forage areas, development of water 

sources, and control of competing animal 

species and people. 

The availability of forage and water within 

and bordering lambing areas is critical. More 

water can be made available by development or 

conservation. Forage can be conserved and 

made available to ewes and young lambs. 

17 
Figure 14.-Reservoirs may submerge habitat suitable for bighorn sheep (photo by Walt Van Dyke, courtesy Oregon Cooperative Wildlife Research Unit). 

Bighorn sheep will tolerate some human intrusion most ofthe year, but the lambing period 

is critical, and the less disturbance the better. 

If a herd has traditional areas for lambing 

(Geist 1971), management should insure that 

travel corridors to such areas are protected and 

maintained. 

FORAGE AREAS 

Plant communities vary widely. Differences 

in species composition and structural features 

are largely the result of past fire and grazing. 

Fire tends to reduce the abundance of shrubs 

and trees, while grasses and forbs are affected 

less or even increased (Franklin and Dyrness 

1973, Graf 1980). Prolonged, heavy grazing by 

18 

livestock has the opposite effect (McQuivey 

1978); grazing pressure is directed to palatable 

plants, and unpalatable plants tend to dominate 

over time (Stoddart et al. 1975). 

Dense shrub and tree canopy or undesirable 

woody plants can be reduced temporarily or 

eliminated by prescribed fire. Bighorn sheep 

select forage areas that have been burned (Geist 

1971, Graf 1980, Peek et al. 1979, Riggs 1977, 

Shannon et al. 1975, Stelfox 1971) (fig. 15). 

Burning may improve plant production and 

palatability (Peek et al. 1979). Logging, chaining, or spraying should give similar results, but 

not as quickly, and debris may present a problem (Morgan 1969, Spalding and Bone 1969, 

Sugden 1961). The goal of any treatment to enhance forage areas is to create the more open 

habitat preferred by bighorn sheep. The extent 

to which mechanical methods of vegetative 

manipulation can be implemented depends on 

geomorphic features and topography. 
Figure 15.-Fire has removed shrub canopy and 

created a suitable forage area (photo by Walt Van 

Dyke, courtesy Oregon Department of Fish and 

Wildlife). 

Conflict between bighorns and other grazing 

species in forage areas appears in two primary 

forms-social interaction and direct competition. Detrimental social interactions have been 

documented between bighorn sheep and cattle 

(Dean 1977, Irvine 1969, Russo 1956, Wilson 

1968) and goats (Russo 1956, Wilson 1968). 

When cattle or goats occupy ranges used by 

bighorn sheep, the sheep move to less desirable 

areas or concentrate on the remaining habitat. 

If bighorn sheep are to be featured, socially conflicting species may have to be removed. Fortunately, the nature of bighorn sheep and thesevere topography they inhabit usually results in 

their isolation from domestic livestock. Adverse 

social interactions between bighorn sheep and 

mule deer, elk, or pronghorns have not been reported in the literature. 

Whenever two or more species of grazing animals are found in the same area, competition for 

forage is possible, but inherent characteristics 

usually allow species to partition a particular 

resource. Competition between. two species may 

be caused by inclement weather, the introduction of exotic ungulates, or tht:! improper management of animal numbers-domestic or wild 

(Crump 1971, Sugden 1961, Weaver 1972). 

There are documented accounts of competition 

for forage between bighorn sheep and cattle 

(Blood 1961, Demarchi 1965, Demarchi and 

Mitchell 1973, Lauer and Pee k 1976, Morgan 

1968, Stelfox 1971); horses (Crump 1971; 

McQuivey 1978; Schallenberger 1965; Stelfox 

1971, 1976; Woodgerd 1964); elk (Buechner 

1969, Cowan 1947, Schallenberger 1965, Stelfox 1971); deer (Berwick 1968, Buechner 1960, 

Cooperrider 1969, Drewek 1970, Morgan 1968, 

Schallenberger 1965, Stelfox 1971); and domestic sheep (Morgan 1968, Uhazy et al. 1971). 

Most of the competition was on bighorn winter 

ranges. In the case of domestic livestock, competition for forage resulted from livestock grazing on bighorn winter ranges dluring summer. 

19 
The result of competition was generally 

twofold-inadequate forage for one or more 

species and severe impairment of range quality. 

Forage allocation and grazing management to 

accommodate bighorn sheep and other grazers 

has been achieved by reducing the number of 

domestic or wild ungulates and/or controlling 

the intensity of domestic livestock grazing and 

season of use (Crump 1957, 1971; Stelfox 1971). 

Similar solutions can be implemented on other 

seasonal ranges. Livestock grazing on bighorn 

range has been completely stopped in some 

areas (Lange et al. 1980). 

Competition for forage is more pronounced 

where livestock grazing occurs on ranges of nonmigratory bighorn sheep. Because of social conflicts and the forage needs of bighorn sheep, it is 

preferable that domestic livestock not be grazed 

within the year-long home ranges of bighorn 

sheep. If grazing by livestock must occur, it 

should be confined to only a portion of the 

bighorn range and periodically moved in a planned grazing system (Anderson 1967). Such action will minimize competition between domestic livestock and bighorn sheep (Anderson and 

Scherzinger 1975). 

The best way to assure an adequate food 

source for bighorn sheep may be to reserve forage areas adjacent to their escape terrain, lambing areas, and water sources. Allowing domestic 

livestock in such areas risks depletion of the 

food supply, which may be limited (Crump 1957, 

1971; Stelfox 1971). Food supplies may also be 

limited by the bighorn sheep's inability or unwillingness to readily change home ranges 

(Geist 1971). 

If domestic livestock are grazed on bighorn 

sheep range, their use should alternate with 

sheep use. Livestock grazing must be done with 

utmost care to insure: adequate forage supplies 

for the sheep at the appropriate season, protection of the range vegetation and soils, and 

minimum harassment of the sheep. These objectives may be attained by fencing, limiting numbers of livestock, grazing on rotational or seasonal systems, placing salt and water to attract 

livestock away from bighorn forage, and using 

fertilizers to improve palatability offorage for 

livestock (Bear 1978, Bodie and Hickey 1980, 

20 

Martin 1978, McCollough et al. 1980, Meehan 

and Platts 1978, Skovlin 1965, Stoddart et al. 

1975). If the management priority is the welfare 

of bighorn sheep, other wild or feral ungulates 

(primarily deer, elk, and horses) may have to be 

reduced by killing or capture and removal to 

maintain sufficient forage for bighorn sheep 

and minimize adverse social interactions. 

Managers will often be faced with problems 

caused by the effects offences on bighorn sheep. 

Fences restrict movement and cause mortality, 

especially of rams that get their horns tangled 

in the wire (Welsh 1971). Helvie (1971) has 

given guidelines for building fences in areas occupied by bighorn sheep. Fences should not be 

constructed with woven wire, but with smooth 

or barbed wire, pipe, rails, or poles. Helvie also 

recommended that posts or stays be placed no 

farther apart than 3 meters (10ft). Wires should 

be spaced 51, 89, and 99 centimeters (20, 35, and ~ 

39 inches) above the ground, and poles, pipes or 

rails 51, 97, and 112 centimeters (20, 38, and 44 

inches) above the ground (fig. 16). Such spacing 

allows bighorns to go through or under a fence 

while restricting livestock movement. 

Another type of fence that can be used is the 

lay-down fence (fig. 16). It can be erected when 

cattle are present and dropped flat when 

bighorn sheep are present. 

Use of fences should allow bighorn sheep to 

move through an area while keeping cattle on 

designated pastures. 

In selecting objectives for managing a range 

for bighorn sheep, a manager should answer 

three questions: (1) What are the requirements 

of the particular bighorn sheep population? (2) 

Do other wild, feral, or domestic ungulates occupy the area with the sheep? and (3) Do these 

occupants alter the habitat in ways that are detrimental to the sheep? Bighorn sheep are a 

much more sensitive part of the management 

equation than mule deer, elk, feral horses, or 

domestic livestock. Bighorn sheep are comparatively rare. They occupy habitats that are 

sensitive to alteration, and they respond 

adversely to disturbance. Unless they are 

given primary emphasis, bighorn sheep are unlikely to become established or to continue in 

existence. 
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Figure 16.- Types and dimensions of fences that can 

be used on bighorn sheep range. 

Bighorn sheep ranges, present and potential, 

occupy such a small percentage of area suitable 

for grazing domestic livestock, that reserving 

forage for bighorn sheep will have little overall 

impact on domestic livestock (fig. 17). 

WATER 

If water is absent or limited on otherwise 

suitable bighorn sheep range, steps can be 

taken to conserve existing water and to make 

new sources available under circumstances that 

encourage bighorn sheep use. 

If water is not available from permanent, 

natural sources, impoundments can be developed to provide it. Water from seeps, lowflow springs, seasonal springs, and seasonal 

streams can be collected, stored, and conserved 

to make it available during critical periods of 

the year (Halloran and Deming 1958, Jones et 

al. 1957, Wilson 1977, Yoakum et al. 1980). 

If water from runoff, springs, or seeps is absent, guzzlers with large collection aprons 

(Yoakum et al. 1980) can be used to collect it (fig. 

18). Water sources that are constructed to collect runoff or seepage water will be most beneficial in ravines or crevices where such water is 

likely to be available. It may be desirable to pipe 

water from a development to troughs-to prevent mucking-or to locations better suited for 

use by bighorn sheep. 

21 
22 

- --

Figure 17 .-In the future, bighorn sheep may depend 

on parcels of land set aside and managed primarily 

for them (photo by Alan Sands). 

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Figure 18.- Water developments that can be installed on bighorn sheep ranges include collection aprons 

with storage tanks and springs or seeps developed 

with troughs. (Adapted from Yoakum et al. 1980) 

PlA":>flC., PIP.,._, ~1-lOUl...U e~ 

~Ufl.,\~0 ']'b PP,~VeNf ~!::Z.IH~ 

DU!l..lt-IC:J Wlt-lfeJZ. AND 

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MA1NTI::r-lb..Nce 
In the Great Basin, naturally occurring 

water is least available during hotter portions 

of the year, after surface water is gone, so impoundments should provide water during this 

period. Where possible, they should be shaded 

from the sun to reduce evaporation. Development of "permanent" water sources can make 

available areas that have all the other components of bighorn sheep habitat (Jones et al. 

1957). During the colder portions of the year, 

water should be available in locations where it 

is least likely to freeze and where the animals 

are most likely to be, such as on south-facing 

slopes. 

Care should be taken to ensure that watering 

devices will not trap or injure bighorn sheep 

(Mensch 1969). Periodic maintenance will be 

needed to keep such devices functioning (Jones 

et al. 1957). 

The most desirable placement of water 

sources is at intervals of 3.2 kilometers (2 mi) 

and within 0.5 kilometer (0.3 mi) of escape terrain. Larger intervals will not allow bighorn 

sheep to use the habitat uniformly and will impose stress on the animals. 

Creating water sources may increase conflict 

between bighorn sheep and other ungulates or 

people. Conditions detrimental to bighorn 

sheep that may result include severe grazing 

(Stelfox 1971); the potential for exchange of 

parasites or disease between bighorns and other 

ungulates, particularly domestic sheep (Bunch 

et al. 1978, Samuel et al. 1975); and degradation 

of water quality by mucking or defecation (Welles and Welles 1961; Wilson 1968, 1977). 

Steps can be taken to remedy such problems. 

Conflicting species can be removed by trapping 

or killing. Existing water holes can be fenced to 

exclude conflicting ungulate species (Morgan 

1969, Schallenberger 1965, Trefethan 1975, 

Wilson 1977). Water sources can be developed 

in rugged topography that only bighorn sheep 

frequent, or other ungulates can be excluded by 

fences while bighorn sheep have access via escape terrain (Halloran and Deming 1958) (fig. .. 19). Water sources for livestock can be installed 

in areas distant from bighorn sheep habitat to 

attract livestock away from such habitat 

(McCollough et al. 1980). 

Figure 19.-Domestic and feral ungulates can bt; 

fenced away from a water source to preserve it for 

bighorn sheep. 

23 
Regular human activity can cause bighorn 

sheep to alter or terminate their use of water 

sources (Blong and Pollard 1968, Buechner 

1960, Welles and Welles 1961). Where this occurs, special restrictions can be implemented 

for people and their equipment (Hicks and Elder 

1979). For best results, water should be conserved and reserved for bighorn sheep through 

proper location and control of conflicting 

species. 

THERMAL FACTORS 

Thermal protection for bighorn sheep comes 

from two primary sources-vegetation and 

geomorphic features. These sources provide 

shade or reradiate heat. A manager must work 

with existing geomorphic features because they 

cannot be produced. Their effectiveness, however, can be enhanced by restricting human activity and insuring that water and forage are 

provided in close proximity to reduce travel for 

bighorns. 

Where trees are lacking, or where trees and 

shrubs have dense or extensive canopies that 

discourage use by bighorn sheep, a manager can 

improve the thermal qualities or use of existing 

stands. Canopies that are too dense can be 

opened by prescribed burning or thinning. If, on 

the other hand, additional cover is needed, 

species compatible with the site, such as mountainrnahognay or juniper, can be planted and 

livestock fenced out to allow seedlings to become established. In arid or semi-arid areas, 

growing trees or tall shrubs is a relatively slow 

process and providing thermal cover may require 10 to 30 years. 

RUTTING AREAS 

Human disturbance is detrimental to breeding. Restricting the use of roads, trails, or areas 

open to travel by people and controlling other 

management activities helps insure that breeding progresses normally. The rut is a critical 

part of the bighorn sheep's life cycle, and solitude is conducive to successful breeding. Excessive disturbance in any form may cause a decline in productivity. 

24 

If a bighorn sheep herd migrates to traditional areas for the rut (Geist 1971), it is of utmost importance that trave1 corridors to such 

areas be protected and maintained. 

PARASITES AND DISEASES 

Some of the factors responsible for the large 

reduction in the number of bighorn sheep since 

the turn of the century have been practically 

eliminated. Indiscriminate shooting has been 

curbed by tightly regulated and enforced hunting systems. In some cases, proper allocation of 

forage between bighorn sheep and other grazers 

has made sufficient forage available for bighorn 

sheep (Crump 1957, 1971; Stelfox 1971). But, 

parasites and diseases are still a threat. 

Numerous parasites and diseases have been 

documented in bighorn sheep (Allen 1971, 

Becklund and Senger 1967). Species-specific 

parasites, such as lungworms and intestinal 

nematodes that have evolved with bighorn 

sheep play a natural role in regulating numbers 

and rarely decimate entire populations (Blood 

1963b, Buechner 1960, Forrester 1971, Kistner 

et al. 1977, McCullough and Schneegas 1966). 

Other co-evolved parasites specific to bighorn 

sheep may not be detrimental to herd health 

(Allen 1971, Samuel et al.1978). 

Although species-specific parasites and diseases may threaten bighorn sheep populations, 

some of the parasites and diseases contracted 

from domestic livestock are a greater threat. 

Although most parasites and diseases carried 

by domestic livestock do not appear to have undesirable effects on bighorn sheep, others apparently have been responsible for decimating 

entire herds. In most of these instances there 

was no direct evidence that domestic livestock 

were the source of the disease or parasite, but 

conditions prevailing at the time suggested that 

domestic livestock were the source. For example, bluetongue, a common disease of domestic 

sheep usually transmitted by insect vectors 

(Trainer 1970), was responsible for the death of 

a captive bighorn sheep in Texas (Robinson et 

al. 1967). Subsequently, the captive herd was 
nearly wiped out by the disease.3 Bluetongue 

also caused the death of several bighorn sheep 

from a herd in northern California (Campbell 

1980). In both instances, domestic sheep had 

ranged in areas adjacent to those used by the 

bighorn sheep. Entire herds in California and 

Washington have recently been lost to bacterial 

pneumonia. The source of the disease probably 

was domestic sheep (Campbell1980, Foreyt and 

Jessup 1982, Jessup 1980). 

The sheep bot fly, usually associated with 

domestic sheep and occasionally with domestic 

goats and deer (Capelle 1971), has been reported in bighorn sheep (Capelle 1966). It was 

recently identified as a cause of mortality in desert bighorn sheep (Bunch et al. 1978). To date, 

there has been no satisfactory way to control the 

spread of the bot fly, whose life cycle can be completed in bighorn sheep. 

The scab mite, which causes psoroptic 

mange, apparently can be carried by domestic 

livestock and at the tum of the century was 

thought to be responsible for significant losses 

ofbighom sheep. Although psoroptic mange has 

since been considered eradicated or controlled, 

it has recently been associated with losses of desert bighorn sheep in New Mexico (Lange 1980, 

Lange et al. 1980, Williams 1980). Because this 

mite can still have drastic effects on herds of 

bighorn sheep, the best prevention is to eliminate opportunities for its transmission from 

domestic livestock. 

Contagious ecthyma (soremouth) has commonly been diagnosed in domestic and bighorn 

sheep (Blood 1971, Campbell 1980, Samuel et 

al. 1975). Although some biologists think this 

condition has minimal impacts on bighorn 

sheep (Blood 1971), it has been responsible for 

numerous deaths, primarily oflambs (Campbell 

1980). 

A species of lungworm common to domestic 

sheep was responsible for deaths in a captive 

herd of bighorn sheep (DeMartini and Davies 

1976, 1977). The animals died from pnuemonia 

that developed only after they were infected by 

the lungworm. 

3 Thomas, Jack Ward, wildlife b10logist, Pacific 

Northwest Forest and Range Experiment Station, 

La Grande, Oregon, personal communication. 

Other parasites and diseases borne by 

domestic sheep that can be harmful to bighorn 

sheep include: helminths (Uhazy and Holmes 

1970); coccidia (Uhazy et al. 1971); and 

pneumonia (DeMartini and Davies 1976, Howe 

et al. 1966, Parks et al. 1972). Pneumonia is 

serious only when bighorn sheep have suffered 

lung tissue damage or are subject to unusual 

physiological or psychological stress (DeMartini and Davies 1977, Woolf and Kradel 1973). 

Any herd of bighorn sheep can become stressed-by predators, by association or competition with livestock or humans, or by inclement 

weather (Foreyt and Jessup 1982, Parks et al. 

1972). 

Therefore, if bighorn sheep are to have the 

best opportunity to survive, they should be spatially separated as far as possible from domestic 

livestock to prevent contamination (Foreyt and 

Jessup 1982, JE:.Ssup 1980, Robinson et al. 1967) 

(fig. 20). This is especially important where flying insect vectors are involved. Attractants 

such as salt stations should be used sparingly 

because they tend to concentrate use by all ungulates and increase the possibility of disease 

transfer (Blood 1971, Samuel et al. 1975). 

Likewise, water sources and feeding stations 

should be placed so they are never used at any 

time by both domestic and bighorn sheep (fig. 

21). 

Pesticides can be used to retard or control 

some outbreaks of disease (Bunch et al. 1978). 

For example, the lungworms of bighorn sheep, 

and the land snails that are the lungworms' intermediate hosts, can be controlled by administering drugs or molluscicides and larvicides to 

animals or by applying the treatment to a range 

(Hibler 1976, 1977; Hibler and Spraker 1976). 

Bighorn sheep infested with scab mites have 

been injected with drugs to kill the mites and 

temporarily prevent reinfestation (Williams 

1981). The difficult step is to catch the bighorns 

so they can be treated. 

25 
26 

---

Figure 20.-Domestic sheep should be kept as far as 

possible from areas inhabited by bighorn sheep 

(photo by Walt Van Dyke, courtesy Oregon Department ofFish and Wildlife). 

Figure 21.-Water sources and salt stations should 

be located so they are not used by both bighorn sheep 

and livestock (photo by Walt Van Dyke, courtesy 

Oregon Department ofFish and Wildlife). 
PREDATION 

Important predators of bighorn sheep in the 

Great Basin include cougar, bobcat, coyote, and 

golden eagle. Of these, the cougar is considered 

the most capable of killing bighorn sheep 

(Buechner 1960, Smith 1954). Most authors addressing this topic indicate that the number of 

animals taken by predators is usually of little 

consequence to healthy populations of bighorn 

sheep (Buechner 1960). Losses frequently can 

be attributed to a single predatory animal that 

can be selectively removed (Blaisdell 1961). 

Predators are most effective when locations of 

eseape terrain or water limit sheep movement 

and allow predators to concentrate hunting effort in a small area (Blaisdell 1961, Light et al. 

1967). The impact of predation must be 

evaluated on a herd-by-herd basis and appropriate action taken. 

HIJMAN IMPACTS 

Even if all the individual components of a 

habitat are satisfactory, the habitat as a whole 

w-ill be unsuitable for bighorn sheep if human 

use is excessive. Human intrusion reduces the 

number of bighorn sheep, by causing sheep to 

reduce or terminate their use of prime habitat, 

stop migration, or split large existing herds into 

smaller herds (Dunaway 1971, Ferrier 1974, 

Horejsi 1976, Jorgensen and Turner 1973, Light 

1B71, Rutherford 1972, Spalding and Bone 

1H69, Weaver 1972, Wehausen 1980, Welles 

and Welles (1961). Human activities responsible for declines in sheep use include hiking and 

backpacking (Blong and Pollard 1968, Dunaway 1971, Nelson 1966, Wehausen 1980, Welles 

and Welles1961), snow skiing (Light 1971), and 

water skiing and fishing (Ferrier 1974). Additional causes of declines are motorbiking (DeForge 1972), driving 4-wheel vehicles (Jorgensem and Turner 1973), construction and use of 

highways (Ferrier 197 4), urban development 

(Ferrier 1974), and 1·ecreational development 

(Spalding and Bone 1969). When bighorn sheep 

are pushed from prime to marginal habitat, 

mortality usually increases and productivitiy 

decreases (Thorne et a l. 1978). 

Some herds of bighorn sheep have become 

conditioned to human activity (Hicks and Elder 

1979). For most herds, however, the amount of 

human activity they can stand varies with the 

herd and the type and amount of activity (Dunaway 1971, Light 1967, McQuivey 1978). Some 

herds have become conditioned to human activity (Hicks and Elder 1979). For example, 

biweekly encounters between bighorn sheep 

and humans may have no measurable effects; 

whereas, daily encounters may cause sheep to 

discountinue use of an area. 

Roads have an important association with 

human activity (Ferrier 1974). Although r oads 

themselves are not necessarily detrimental to 

bighorn sheep, they greatly facilitate human 

access (fig. 22). Backcountry roads that receive 

little use may have little or no effect, but other 

roads have caused bighorn sheep to alter traditional migration routes (Ferrier 1974). Roads 

must be individually evaluated. If human access is detrimental, it can be controlled through 

road closures. When bighorn sheep are on summer range, human use of roads on their winter 

range will have little effect. The opposite is also 

true. Where bighorn sheep occupy year-long 

ranges, permanent road closures should be 

considered. 

Road closures may not be feasible when 

bighorn sheep ranges lie adjacent to major roads 

or highways, but restricting off-road use of such 

areas may be feasible. 

Remote, roadless bighorn sheep ranges 

sometimes receive heavy daily use from hikers 

and backpackers. In such situations, closures or 

restrictions may be required. 

Land developments such as resorts, housing 

subdivisions, private dwellings, and hydroelectric installations, and activities such as mining, 

logging, and road construction, cause bighorn 

sheep to alter their use ofhabitat (Ferrier 1974, 

McQuivey 1978, Sugden 1961, Yoakum 1971). 

If the management objective is to maintain 

bighorn sheep, a careful evaluation of potential 

habitat alteration and human activity is critical 

to the planning process. For the most part, 

bighorn sheep now exist in the wild because of 

human decisions, and the fate of the species in 

the Great Basin of southeastern Oregon and 

other areas will be determined by future management of public lands (fig. 23). 

27 
28 

Figure 22.-Roads through prime bighorn sheep 

habitat increase human access and associated negative impacts (photo by Walt Van Dyke). 

Figure 23.-The future of bighorn sheep depends on 

the response of people to the bighorns's needs (photo 

by Walt Van Dyke, courtesy Oregon Cooperative 

Wildlife Research Unit). 
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Appendix 

Common name 

Common and Scientific Names 1 

Scientific name 

MAMMALS 

Bighorn sheep 

California bighorn sheep 

Cougar 

Coyote 

Deer 

Desert bighorn sheep 

Domestic cow 

Domestic goat 

Domestic sheep 

Horse 

North American elk 

Pronghorn 

Rocky Mountain bighorn sheep 

Golden eagle 

Antelope bitterbrush 

Arrowleafbalsamroot 

Aspen 

Basin big sagebrush 

Bearded bluebunch wheatgrass 

Big sagebrush 

Black greasewood 

Black sagebrush 

Blue elderberry 

Bluegrasses 

Bolander silver sagebrush 

Bottlebrush squirrel tail 

Bud sagebrush 

Cheatgrass brome 

Cherry 

Chokecherry 

Cinquefoil 

Cleftleaf sagebrush 

Cobre rockcress 

Common snow berry 

Common winterfat 

Cottonwood 

Cream bush rockspirea 

Curlleafmountain-mahogany 

Ovis canadensis 

Ovis canadensis californiana 

Felis concolor 

Canis latrans 

Odocoileus spp. 

Ovis canadensis nelsoni 

Bostaurus 

Capra hircus 

Ovisaries 

Equus caballus 

Cervus elaphus 

Antilocapra americana 

Ovis canadensis canadensis 

BIRDS 

Aquila chrysaetos 

PLANTS 

Purshia tridentata 

Balsamorhiza sagittata 

Populus spp. 

Artemisia tridentata tridentata 

Agropyron spicatum 

Artemisia tridentata 

Sarcobatus vermiculatus 

Artemisia nova 

Sambucus cerulea 

Poaspp. 

Artemisia cana bolanderi 

Sitanion hystrix 

Artemisia spinescens 

Bromus tectorum 

Prunusspp. 

Prunus virginiana 

Potentilla fruiticosa 

Artemisia arbuscula thermopola 

Arab is cobrensis 

Symphoricarpus albus 

E urotia La nata 

Populus spp. 

Holodiscus discolor 

Cercocarpus ledifolius ledifolius 

1 Mammal names from Chapman and Feldhammer (1982); bird names from American Ornithologist's Union (1957); plant names from Garrison et al. (1976); parasite and disease names 

from Davis et. a!. (1970). 

35 
36 

Appendix (continued) 

Common name 

Currant 

Cushion buckwheat 

Douglas-fir 

Early low sagebrush 

Erigeron 

Fairway crested wheatgrass 

Fir 

Fourwing saltbush 

Giant wildrye 

Idaho fescue 

Indian ricegrass 

Juniper 

Lomatium 

Low sagebrush 

Lupine 

Mallow ninebark 

Meadow barley 

Milk vetch 

Mountain big sagebrush 

Mountain-mahogany 

Mountain silver sagebrush 

Mountain snow berry 

Penstemon 

Phlox 

Pine 

Pinegrass 

Pinnate tansym ustard 

Prairie junegrass 

Quaking aspen 

Rabbitbrush 

Rose 

Sagebrush 

Saskatoon serviceberry 

Sedge 

Shadscale saltbush 

Shiny leaf spiraea 

Spiny hopsage 

Squaw apple 

Subalpine big sagebrush 

Threetip sagebrush 

Thurber's needlegrass 

Wallflower phoenicaulis 

Western juniper 

Wild buckwheat 

Willow 

Wyoming big sagebrush 

Yarrow 

Scientific name 

Ribes spp. 

Eriogonum ovalifolium 

Pseudotsuga menziesii 

Artemisia longiloba 

Erigeron spp. 

Agropyron cristatum 

Abies spp. 

A triplex canescens 

Elymus cine reus 

Festuca idahoensis 

Oryzopsis hymenoides 

Juniperus spp. 

Lomatium spp. 

Artemisia arbuscula arbuscula 

Lupinus spp. 

Physocarpus malvaceus 

Hordeum brachyantherum 

Astragalus spp. 

Artemisia tridentata vaseyana 

Cercocarpus spp. 

Artemisia cana sub. viscidula 

Symphoricarpus oreophilus 

Penstemon spp. 

Phloxspp. 

Pinusspp. 

Calamagrostis rubescens 

Descurainia pinnata 

Koeleria cristata 

Populus tremuloides 

Chrysothamnus spp. 

Rosaspp. 

Artemisia spp. 

Amelanchier alnifolia 

Carexspp. 

A triplex confertifolia 

Spiraea lucida 

A triplex spinosa 

Peraphyllum ramosissimum 

Artemisia tridentata form spiciformis 

Artemisia tripartata 

Stipa thurberiana 

P hoenicaulis cheiranthoides 

Juniperus occidentalis 

Eriogonum spp. 

Salixspp. 

Artemisia tridentata wyomingensis 

Achillea millefolium 
Appendix (continued) 

Common name Scientific name 

Bacteria 

Lungworms 

Nematodes 

Scab mite 

Sheep bot. fly 

PARASITES AND DISEASES 

Corynebacterium pogenes 

Pasteurella multocida 

Muelleruis sp. 

Protostrongylus stilesi 

Protostrongylus rushi 

Nematodirus spp. 

INSECTS 

Psoroptes avis 

Oestrus avis 

37